The present invention relates to a driving device for displacing an element in a conduit filled with liquid.
The term element is used here to designate tools such as scraping tools, mini-corers, etc., measuring instruments, such as a measuring sonde, or any other element which, at a given time, must be displaced within a conduit.
The term conduit is used here to designate either conduits formed by tubes or wells drilled in the ground by any suitable method.
Devices for displacing tools within a conduit are already known and described, for example, in U.S. Pat. No. 3,052,302.
These prior art devices generally comprise a body having an extension to which above-discussed tool is connected.
One, or several inflatable sleeves surround the body and seal an annular space between the body of the device and the wall of the conduit wherein the device is employed.
The displacement of such a device is achieved by pumping the fluid which fills the conduit and this requires access to both ends of the conduit.
Such prior art devices are therefore not suitable for displacing an element such as a measuring sonde in a wellbore during drilling operations.
The use of inflatable membranes in wellbores is also known from U.S. Pat. No. 3,960,211 which describes a device adapted to take an impression of the wall of a casing, or from U.S. Pat. No. 3,209,835 which describes an inflatable packer adapted to isolate a portion of a wellbore. Inflatable sleeves are also described in U.S. Pat. Nos. 2,942,667 and 2,946,565 for sealing the annular space between a borehole wall and a drill string, so as to isolate the zone of the borehole which is just above the drill bit, and to adjust the pressure of the drilling fluid to a selected value in this portion of the borehole.
These sleeves are slidable along the drill string and move stepwise under the influence of gravity while enabling the drilling operation to progress after the sleeves have been inflated to make them integral, or place them in contact, with the borehole wall.
These prior devices are therefore not adapted to displace an element in a conduit of high inclination relative to a vertical line, in particular in a subhorizontal conduit, because the influence of gravity then can no longer provide for a stepwise displacement of the slidable sleeve.
In practice an element such as a measuring sonde can be displaced by the influence of gravity without great difficulty as long as the inclination of the drilled well relative to a vertical line is not substantially greater than 45.degree.. Beyond this limit the displacement of the sonde is possible only if the profile of the drilled hole and the variations of its diameter are known, and if sondes of a reduced size are used. In highly inclined boreholes the displacement of the sonde can only be obtained by applying a thrust thereon by means of a relatively stiff rod at one end of which the sonde is connected.
However, displacing a sonde in a wellbore remains an operation whose duration and difficulty increases with the angle of inclination of the wellbore relative to the vertical line.
In order to obviate these drawbacks, it has been proposed, in U.S. Pat. No. 4,113,236, to provide a jet propulsion device to which is connected the element to be displaced. A disadvantage attendant to this device is that considerable power has to be transmitted to the device to produce sufficiently efficient fluid jets, capable of displacing an element in a wellbore of high inclination relative to the vertical axis. Moreover, the operation of such a device is not reversible and the displacement can only be effected in one direction. Furthermore, the fluid jets have deleterious effects on the borehole wall when the latter is not protected by a casing.
The main object of the invention is therefore, to provide a device which does not suffer from the above-discussed disadvantages, and permits displacement of an element within a conduit of high inclination relative to the vertical axis, or a conduit having horizontal sections, or even portions along which the device is displaced against the influence of gravity.